clarify calculus notes

diff --git a/spec/calculus.md b/spec/calculus.md
index 2b68bf5692bec02045cdccc1b1d81146c69ecd72..3823f37d7dbfc72d5eb0596b20a963276bb03c39 100644 (file)
--- a/spec/calculus.md
+++ b/spec/calculus.md
@@ -145,11 +145,11 @@ $\log_b y^{x^n} = x^n \log_b y$
 
 ### $e$ as a logarithm
 
-$$\log_e e = 1$$
+$$\operatorname{if} y=e^x, \quad \operatorname{then} x=\log_e y$$
 $$\ln x = \log_e x$$
 
 ### Differentiating logarithms
-$${d \over dx} \log_b x = {1 \over x \ln b}$$
+$${d(\log_e x)\over dx} = x^-1 = {1 \over x}$$
 
 ## Solving $e^x$